1. Field of the Invention
The present invention relates generally to a semiconductor device and, more particularly, to a semiconductor device including a high voltage generation circuit and a method of generating a high voltage.
A claim of priority is made to Korean Patent Application No. 10-2006-0094799, filed on Sep. 28, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
2. Description of the Related Art
A flash memory device is considered a non-volatile memory device in that it retains data stored when power to the device is turned off or otherwise interrupted. While many types of semiconductor memory devices utilize a single power supply unit, a flash memory device typically requires the generation of multiple internal voltage levels in order to drive different types of circuits included within the device.
For example, a program voltage for programming data in a flash memory cell and an erase voltage for erasing data from the flash memory cell are generally higher than a power supply voltage (e.g., 20V). In addition, a voltage of about 5-8 V may be needed during a read operation.
In order to obtain these voltages, the flash memory device generally includes a high voltage generation circuit. Specifically, the high voltage generation circuit generates a constant voltage. The high voltage generation circuit may be referred to as a regulator circuit and is usually implemented using a charge pump. The high voltage generation circuit may also be used to generate voltages having different levels. This may be achieved, for example, by receiving a single power such as a first power supply voltage and generating different power supply voltages having different voltage levels using the voltage regulator circuit.
For example, in a semiconductor memory device, a second voltage generation unit included in the device boosts a first voltage. This first voltage is typically provided from an external power source. The boosted first voltage may be referred to as a second voltage. Generally, the first voltage is boosted to the second voltage using a first charge pump.
The semiconductor memory device may also include a third voltage generation unit. The third voltage generation unit outputs a third voltage (e.g., a program voltage) using the second voltage and a second charge pump. Furthermore, the second voltage is higher than the externally applied first voltage and is used to control a switch which is implemented in the third voltage generation unit to enable the third voltage to attain a target level.
The third voltage generation unit also includes a resistor divider. This resistor divider usually controls the increase and the decrease of an output voltage. Furthermore, a current path for the resistor divider is controlled by a switch. In particular, the switch is connected in parallel with the resistor divider and is turned on or off in response to the second voltage generated by the second voltage generation unit and a switch enable signal.
Typically, the semiconductor memory device maintains the second voltage higher than the third voltage and uses the second voltage as a power supply voltage for driving at least one circuit included therewithin. For example, when the semiconductor memory device is a flash memory device, the switch in the second voltage generation unit is controlled by the second voltage to output the third voltage having a predetermined target level. The third voltage may be used for various tasks. For example, the third voltage may be used as a program voltage for programming data in a cell, a voltage for verifying data programmed in the cell, a voltage for erasing data from the cell, or a voltage for verifying the erasure of the data from the cell.
While the conventional semiconductor device may use different voltage generation circuits to generate different voltages at different levels, it suffers from various shortcomings. For example, when a load capacitance at an output terminal of the second voltage generation unit (e.g., a parasitic capacitance at a bus line) is greater than a load capacitance at an output terminal of the third voltage generation unit, the third voltage may increase quickly to be higher than the second voltage. This kind of increase in the third voltage may result in an overshooting of the third voltage. This overshooting of the third voltage may cause the semiconductor memory device to operate abnormally.